As ink jet recording system, there are known various ink jet recording systems such as a system (electric field controlling system) in which ink is discharged using electrostatic attraction, a system (drop-on-demand system or pressure pulse system) in which ink is discharged using the oscillation pressure of a piezoelectric element, and a system (bubble or thermal system) in which ink is discharged using pressure developed by forming bubbles and allowing them to grow with heat. By any one of these systems, highly detailed images can be obtained.
In these ink jet recording systems, aqueous ink using water as a main solvent, and oil-based ink using an organic solvent as a main solvent are generally used. Matters printed with aqueous ink are generally poor in water resistance and printing with the aqueous ink on recording media having water-proof surface is difficult. On the other hand, oil-based ink has advantages that it can provide printed matters which are excellent in water resistance and that it can facilitate the printing on recording media having water-proof surface or wood free papers. Further, oil-based ink using pigment as colorant is excellent in light stability.
In conventional oil-based ink, however, an aromatic hydrocarbon such as toluene or xylene, an aliphatic hydrocarbon such as hexane or kerosene, a ketone group such as methyl-ethyl ketone, an ester group such as ethyl acetate, or propylene glycol mono-methyl ether acetate is generally used as organic solvent. However, the oil-based ink has the following problems. When printing is conducted on a polyvinyl chloride substrate as a recording medium with such an ink using organic solvent as mentioned above, nozzles are easily clogged because such an organic solvent has low boiling point and low flash point so as to easily dry. In addition, it is expensive to satisfy the printer specification because of the dissolving and swelling properties of such an organic solvent relative to plastics (for example, polystyrene resin and ABS resin) used in ink storage containers, apparatuses such as a printer, and parts thereof. Further, when printing is conducted on a polyvinyl chloride substrate, such oil-based ink cannot provide satisfactory print quality nor provide satisfactory dry characteristics of printed matter.
It is an object of the present invention to provide an oil-based ink composition for ink jet recording which can be suitably used for printing on a polyvinyl chloride substrate and is excellent in all of print quality, printing stability, dry characteristics of printed matter, and storage stability of ink.